The Army should continue equipping troops with its standard 5.56 mm rifle round because the ammo is well-suited for close-quarter firefights with insurgents in Iraq and Afghanistan, according to officials at the service's Picatinny Arsenal.

In a recently completed multiyear study, weapon testers at the New Jersey-based organization compared the round, dubbed "M855," with seven other military and commercial 5.56 mm variants, according to Army Col. Mark Rider, the project manager for small- and medium-caliber ammunition at Picatinny.

The assessment examined whether there is a more effective 5.56 mm round against unarmored enemies -- called "soft targets" in military jargon -- at ranges of up to 50 meters, he told sister publication Inside the Pentagon May 26.

The standard 5.56 mm round, used by NATO militaries and sometimes called "Green-Tip" because of its colored top, is widely used by U.S. units operating inside Iraq and Afghanistan. The round has a "grain" of 62.

The Army conducted its assessment in response to numerous reports from troops deployed overseas. Service members alleged that the standard 5.56 mm round is unable to stop the advance of attacking enemies at close ranges because the bullets penetrate their bodies, rather than rendering them unable to continue their charge.

Army testers compared the M855 with four commercial-off-the-shelf rounds, ranging in grain from 62 to 100, said Army Lt. Col. Matthew Butler, a member of the assessment team. They also tested three military versions: the 55-grain M193; the 77-grain Mk262; and the 52-grain armor-piercing M995, he said in the same May 26 interview.

During the experiments, testers fired bullets at gel blocks and used computer modeling and simulation techniques to study how the rounds behave under different conditions, according to briefing slides released by the Army.

The tests revealed that all variants of the 5.56 mm ammunition performed "comparably" when fired from the Army's M16 and M4 rifles. The experiments also showed that none of the alternative munitions would offer significant advantages over the standard M855, Rider said.

The recent experiments also provide an explanation for why some troops have reported literally shooting straight through the bodies of enemy fighters in Iraq and Afghanistan without stopping them, according to Butler.

The tests revealed to Picatinny officials that the reason lies in the angle at which a bullet hits its human target, he noted. While the M855 ammunition is designed to take a straight flight path, individual bullets may slightly drift up or down right before making impact, he said.

Those bullets that hit their targets straight on traveled up to 7 inches inside the gel blocks before they mushroomed, while those with a few degrees of yaw did so sooner, Butler said. Drifting bullets could pass completely through a slim person's body if its misses that individual's bones, he added.

"That really is the phenomenon that explains the through-and-throughs," Butler said.

The Army testers said knowing where to shoot an enemy is crucial.

"The only real guaranteed put-down [shot] is the central nervous system -- the head, the neck, the upper torso," according to Butler. "Other than that, even if you hit [an adversary] in the spine below that central area, the arms still work" -- and the motivation to attack remains, he added.

"What soldiers need is an off-button," Butler said.

The service should continue to "emphasize" live-fire training to exercise "proper shot placement," Rider said. Traditionally, troops are trained to aim at the center mass of the torso, according to Butler. At distances of 10 meters or less, however, troops should aim higher to increase the chance of "incapacitation," Rider said.

The concept of aiming higher at such short distances is "counterintuitive" and it "may be hard to train," according to the briefing slides.

Troops should use the "controlled pair" shooting technique -- two shots in rapid succession -- to increase accuracy, the officials said. "In the study itself, it showed that lethality is increased by [10 to 20 percent] percent if you use those controlled pair shots, vice just a single, well-aimed shot," Butler said.

In its assessment, the Army teamed up with the Marine Corps, special operations forces, the FBI, the Department of Homeland Security, as well as military and civilian research institutions, according to the briefing slides.

The Army study comes after several warfighter reviews lobbed criticism at the NATO-wide 5.56 mm round. One of those was a May 17, 2005, report penned by the commanding officer of Company F (Fox), 2nd Battalion, 24th Marine Regiment, 4th Marine Division.

The Fox Company, whose experiences with the round are detailed in the 24-page assessment, is a Marine Reserve unit based in Milwaukee, WI. The outfit was deployed to Iraq from September 2004 to April 2005. The unit was positioned near Yusufiyah, a town located southwest of Baghdad, according to the report. The company was responsible for over 200 square kilometers, much of which was considered "hostile territory" and the home of "hostile tribes," according to the document.

"During engagements of less than 100 meters, [enemies] shot multiple times in the torso with 5.56 seemed to continue to function for a long period of time," the Fox Company assessment reads. "Head shots seemed to be the only way to kill someone quickly" with the Green-Tip bullet, it continues.

Meanwhile, Marine Corps officials are in the final stages of their own study of ammunition performance, according to Col. Clarke Lethin, the director of the fires and maneuver integration division at Marine Corps Combat Development Command in Quantico, VA. MCCDC hopes to wrap up that study by the end of June.

The Marine Corps' assessment is aimed identifying what type of ammunition is best-suited to penetrate barriers -- like vehicle doors or windshields -- while still achieving "desired effects," Lethin said May 30.

The study considers larger calibers than the 5.56 mm round, he said. For example, Marine testers are looking at 7.62 mm bullets, among others, he said.

Determining whether a larger-caliber round makes sense for deployed Marines will depend on a number of factors, Lethin said. For one, the weight of a new type of cartridge is an important criterion, he said. Also, the amount of ammunition a Marine can carry on the battlefield is another crucial factor, he added.

Finally, industry would have to be able to offer a rifle that can shoot the larger-caliber bullets, according to Lethin. "I can buy an elephant gun but can industry support that?" -- Sebastian Sprenger